- Email: [email protected]
Comparison of crown fit and operator preferences between tooth preparation with electric and air-turbine handpieces
RESEARCH AND EDUCATION
Comparison of crown fit and operator preferences between tooth preparation with electric and air-turbine handpieces Dan-dan Pei, MD,a Yu-chen Meng, BS,b Ahmed S. Fayed, MS,c Yu-fei You, MS,d Zi-xiao Wu, BS,e and Yi Lu, PhDf
ABSTRACT Statement of problem. Tooth preparations for ceramic crowns require precision and accuracy, which may be influenced by the choice of dental handpiece. However, comparisons of the accuracy of tooth preparations made with traditional air-turbine handpieces and electric handpieces are lacking. Purpose. The purpose of this in vitro study was to evaluate operator preferences and tooth preparation performance by using electric and airturbine handpieces with self-reported preferences, sound levels, surface roughness, and the fit of the crown produced. Material and methods. Twenty dentists were asked to use the air-turbine or the electric handpiece. Feedback on the noise, weight, feel of grip, flexibility, and tooth preparation in general was scored according to a visual analog scale (VAS). Additionally, the dentists were asked to complete a questionnaire on their handpiece preference. The noise of the 2 handpieces was measured by using a precision sound level meter. The surface roughness of 10 teeth was measured by using a profilometer. The other 18 teeth were prepared to measure the marginal and internal fit of ceramic crowns by the replica technique. The VAS scores of operator preferences were analyzed with the Wilcoxon signed ranks test. Decibel levels were analyzed with the Mann-Whitney U test. The McNemar test was used to compare the ratio of preferred handpiece. The surface roughness and marginal and internal fit were analyzed with the independent t test to determine significant differences (all a=.05). Results. The electric handpiece was heavier, had a poorer grip feel, was less flexible (P<.001), produced lower noise and better feeling of the tooth preparation in general (P<.001), and was preferred in the finishing stage for its greater smoothness (P<.05). The noise produced by the electric handpiece was lower during both idling and tooth preparation at 15-cm, 30-cm, and 45-cm distances (P<.01). The electric handpiece produced surface roughness values (Sa) similar to those of the air-turbine handpiece (P>.05). No significant differences were noted for the marginal and internal crown fit between the air-turbine handpiece and electric handpiece groups (P>.05). Conclusions. Despite its heavier weight, poorer grip feel, and less flexibility, the electric handpiece emitted lower noise, produced better feeling of the tooth preparation in general, and was preferred in the finishing step of tooth preparation for its greater smoothness than the air-turbine handpiece. The surface roughness of the prepared teeth and the crown fit between the tooth and ceramic crown were not affected by the air-turbine or electric handpiece. (J Prosthet Dent 2019;-:---)
A high-quality tooth preparation is essential for producing a precision crown restoration in contemporary dentistry, with the choice of dental handpiece being an important factor affecting the accuracy of the tooth preparation.1 The traditional high-speed air-turbine handpiece has been used in dentistry for decades,2 and
although they are still extensively used, their low torque can cause a loss of speed (revolutions per minute) and even stall at moderate or high load.3 Dentists have also complained about other deficiencies, including the high-pitched noise,4-6 vibration, and poor concentricity.7 To overcome these disadvantages, electric
D.-d.P. and Y.-c.M. contributed equally to the work. This study was supported by grants from the National Natural Science Foundation of China (grant #81870798), the Innovation Project from Shaanxi province (grant #2016KTCL03-10), and the opening project from College of Stomatology, Xi’an Jiaotong University (grant #2018YHJB07). a Associate Professor, Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. b Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. c Former Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. d Former Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. e Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. f Professor and Chair, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China.
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Clinical Implications Tooth preparation with an electric or air-turbine handpiece did not affect the fit of a ceramic crown. However, the significantly heavier electric handpiece was significantly quieter and smoother than the air-turbine handpiece.
motors with speed-increasing handpieces have been introduced. Compared with air-turbine handpieces, electric handpieces have a smoother operation because of their constant power and high torque,1,7 which may provide clinicians with greater tactile feedback for a more controlled cutting performance, especially for the creation of margins. Conversely, the increased size and weight of electric handpieces are shortcomings, particularly for dentists with smaller hands.8,9 When selecting a handpiece, the working efficiency, operator preference,10 and preparation results are parameters that dentists consider. Recent studies of electric handpieces have mainly focused on the cutting efficiency, and the results have demonstrated that electric handpieces are comparable or even more efficient at cutting dental hard tissue than airturbine handpieces.2,11 However, the user’s feeling and the tooth preparation performance of electric handpieces have not yet been clarified in detail. The demand for esthetics has made ceramic restoration a popular choice.12-14 The marginal and internal accuracy of fit are important criteria for the clinical success of ceramic prostheses.15,16 Thus, the present study evaluated the operator preferences and tooth preparation performance of electric handpieces compared with those of traditional air-turbine handpieces. The sound levels produced by handpieces, self-reported preferences, surface roughness, and crown fit of electric and air-turbine handpieces were evaluated to assist dentists in their choice. The null hypotheses were that no differences would be found in the operator preference scores, preference ratios, sound levels, surface roughness, or crown fit between teeth prepared with electric or air-turbine handpieces. MATERIAL AND METHODS An electric handpiece (Restorative Classic CA 1:5; BienAir Dental) and an air-turbine handpiece (TE-95RM; W&H Dentalwerk GmbH) were used for the tests. The electric handpiece was used at its maximum speed of 200 000 revolutions per minute (40 000 motor speed with a 1:5 ratio).3 A total of 54 intact impacted human third molars were obtained from the Department of Oral and Maxillofacial Surgery, School and Hospital of Stomatology, Xi’an Jiaotong University, after informed consent THE JOURNAL OF PROSTHETIC DENTISTRY
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was obtained from the donors and approval by the ethics committee. The teeth were stored in 0.02% sodium azide at 4 C for less than 3 months before use. To evaluate the operator preferences, 20 experienced dentists from the Department of Prosthodontics, School and Hospital of Stomatology, Xi’an Jiaotong University, were enrolled in the study. The range of clinical experience varied from 6 to 20 years (with a mean clinical experience of 15.4 years). The dentists were instructed to use the air-turbine or electric handpiece with hand grip gestures (Fig. 1) during idling and tooth preparation and to record their user experiences. Feedback in terms of noise level, weight, feel of the grip, flexibility, and general feeling of the tooth preparation was scored according to a visual analog scale (VAS). The dentists were asked to complete a questionnaire on their handpiece preference for the initial preparation, finishing preparation, and smooth operation. All measurements were conducted in a separate room with good sound insulation to exclude environmental interference. The handpiece noise emission was detected by using a precision sound level meter (6288; Aihua Instruments Co, Ltd).17 The sound levels during handpiece idling were first measured at 15-cm, 30-cm, and 45-cm distances from the prepared tooth for each handpiece. The sound levels during tooth preparation with salivary suction were then measured at 15-cm, 30-cm, and 45-cm distances from the prepared tooth. The noise measurement for each group was repeated 6 times, and each interval was 5 seconds. To measure the surface roughness after tooth preparation, 10 teeth were divided into air-turbine and electric handpiece groups and prepared on dental simulators (NISSIM Type 1; NISSIN) by the same operator (D.-d.P.) with 6 years of clinical experience following complete crown preparation guidelines18 with new diamond rotary instruments (Table 1). The surface roughness of the prepared specimens was then evaluated quantitatively by using a profilometer (PS50; Nanovea). The sensor was placed perpendicular to the tooth surface. Three measurements were analyzed for each specimen, and each measurement area was 280×210 mm. A 60×60-mm Gaussian filter was used to remove errors. The mean surface roughness of each specimen was represented by Sa values.19 The crown fit test was conducted by evaluating the marginal and internal fit of ceramic crowns. A total of 18 teeth were divided into 2 groups. Following the complete crown preparation guidelines, the teeth were prepared in manikin heads with the air-turbine or electric handpiece by the same operator (D.-d.P.) with 6 years of clinical experience. After finishing the tooth preparations, Cercon II ceramic crowns (Dentsply Sirona) with a preset internal gap space of 80 mm in the occlusal and axial plane and 20 mm at the margins were designed and Pei et al
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Figure 1. A, Air-turbine handpiece. B, Electric handpiece. Table 1. Characteristics of diamond rotary instrument used Diameter of Diamond Particles (mm)
Manufacturer
Number
Coarse
125
Diatech
856-314-014-9-ML
Coarse
125
Diatech
881-314-012-8-ML
Coarse
125
Diatech
379-314-023-5-ML
Fine
40
Diatech
856-314-016-8-F
Extra fine
20
Diatech
379-314-023-5-XF
Extra fine
20-30
MANI
TR-25EF
fabricated by the same technician for each individual abutment tooth. Then, the marginal and internal fit of each crown was measured as the internal gap between the crown and the prepared tooth by using the replica technique with silicone impression material (HonigumLight, Honigum-Putty; DMG) as described previously.15,20 Briefly, each crown was filled with a yellow light-body silicone material and placed onto the corresponding tooth under a constant force of 50 N. After polymerization for 5 minutes, the tooth was carefully removed, and purple heavy-body silicone rubber material was then applied instead of the prepared tooth. Finally, the crown was removed, and the purple heavy-body silicone rubber material was applied on the crown side to form a sandwich silicone replica. The replicas were cross-sectioned into thicknesses of 1 mm at the center of and perpendicular to the occlusal surface. These sections were measured at ×100 magnification under a stereomicroscope (M250FA; Leica) by 1 blinded investigator (Y.-c.M.). The light-body thickness represented the discrepancy between the crown surface and the abutment tooth. Measurements were conducted at 10 points by following an established protocol21 as shown in Figure 2: A1 and A2 represent the marginal discrepancy; B1 and B2 represent the shoulder discrepancy; C1, C2, D1, and D2 represent the axial discrepancy; and E1 and E2 represent the occlusal discrepancy. All the statistical calculations were conducted by using a statistical software program (PASW Statistics, v18.0; Pei et al
Figure 2. Sites of evaluation of crown fit. A1, A2: margin. B1, B2: shoulder. C1, C2, D1, D2: axial wall. E1, E2: occlusal surface.
Groups
Grit
Tooth preparation feeling
*
Flexibility
*
Hand grip feeling
*
Weight
*
Noise of preparation
*
Noise of idling
* 0
2
4
6
8
10
Index Electric handpiece
Air-turbine handpiece
Figure 3. VAS scores of operator preferences for air-turbine and electric handpieces. *Statistically significant (P<.05).
SPSS Inc) (a=.05). The Wilcoxon signed-rank test was used to compare the differences in the VAS scores of the operator preferences because the paired data did not satisfy the parametric methods. The McNemar test was used to compare the paired ratios of the preferred handpiece. The independent decibel level data did not satisfy the parametric methods, so the Mann-Whitney U test was applied to the analysis. Statistical analyses of the THE JOURNAL OF PROSTHETIC DENTISTRY
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Preference in initial preparation
Electric 35%
70
* *
60 55 15
30
45
Traverse length (cm) Air-turbine handpiece
Electric handpiece
A
A dB 75
Sound level (dB)
Preference in finishing preparation
Both 10%
*
*
70
*
65 60 55 50
Electric 80%
15
30
B
Electric handpiece
B Figure 5. Sound levels of air turbine and electric handpieces at 15-cm, 30-cm, and 45-cm distances. A, During idling. B, During tooth preparation. *Statistically significant (P<.05).
Preference in smooth operation
Both 10%
Electric 80%
C Figure 4. Distribution of total variables. A, Initial preparation. B, Finishing preparation. C, Smooth operation.
surface roughness and marginal and internal fit were performed by using the independent t test after the normal distribution and homogeneity of variance tests. RESULTS The VAS scores of the operator preferences are illustrated in Figure 3. The Wilcoxon signed-rank test indicated that THE JOURNAL OF PROSTHETIC DENTISTRY
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Traverse length (cm) Air-turbine handpiece
Air-turbine 10%
-
*
65
50
Air-turbine 50%
Air-turbine 10%
Issue
dB 75
Sound level (dB)
Both 15%
-
the air-turbine handpiece noise was significantly higher than that of the electric handpiece both during idling (Z=-5.377, P<.001) and tooth preparation (Z=-5.446, P<.001), while the electric handpiece was relatively heavier than the air-turbine handpiece (Z=-5.377, P<.001). The air-turbine handpiece was better than the electric handpiece in terms of grip feel (Z=-5.452, P<.001) and flexibility (Z=-5.519, P<.001), while the electric handpiece was better than the air-turbine handpiece for general tooth preparation (Z=-5.516, P<.001). The ratio of the dentists’ preferred handpieces varied significantly for the initial preparation, finishing preparation, and smooth operation (P<.05). Figure 4 illustrates the distribution of the total variables on the 3 questions. Although only 35% of the dentists chose the electric handpiece, 15% thought both handpieces were acceptable during initial preparation, while 80% preferred the electric handpiece for finishing. Overall, 80% of the dentists reported that the electric handpiece offered smooth operation in the working process. The mean values and standard deviations of the sound levels measured at 15-cm, 30-cm, and 45-cm Pei et al
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Figure 6. Three-dimensional surface profile. A, Air-turbine handpiece group. B, Electric handpiece group.
Table 2. Gap thickness (mean ±standard deviation) between crown and abutment tooth after preparation by air-turbine and electric handpieces (n=9) Marginal Groups
Internal
Marginal (A)
Shoulder (B)
Axial (C)
Axial (D)
Occlusal (E)
Total
Air-turbine
116.1 ±13.4
123.7 ±24.0
84.5 ±20.7
101.1 ±26.7
210.6 ±27.0
130.0 ±17.0
Electric
106.5 ±12.3
137.5 ±13.5
73.3 ±21.1
107.1 ±22.5
186.8 ±27.7
126.2 ±14.0
No significant difference among groups (P>.05).
distances from the prepared tooth are shown in Figure 5. The highest decibel level was produced by the air-turbine handpiece at the15-cm distance during tooth preparation, and the lowest decibel level was produced by the electric handpiece at the 45-cm distance during idling. The statistical analysis revealed significant differences in the decibel levels produced by the 2 handpieces during idling at the 15-cm (Z=-2.908, P<.01), 30-cm (Z=-2.882, P<.01), and 45-cm (Z=-2.908, P<.01) distances. The decibel levels of tooth preparation were also significantly different between the air-turbine handpiece and electric handpiece at the 15-cm (Z=-2.898, P<.01), 30-cm (Z=-2.934, P<.01), and 45-cm (Z=-2.898, P<.01) distances. The tooth surface roughness prepared by the airturbine handpiece had Sa values (mean ±standard deviation) of 1.58 ±0.18, and the Sa values of the electric handpiece were 1.49 ±0.25. No statistically significant difference for Sa was found (t=0.908, P>.05). Figure 6 presents 3D graphs (scale: x-axis 0.005 mm per mark, y-axis 0.002 mm per mark, and z-axis 0.01 mm per mark) of the surface microstructure. The air-turbine handpiece and electric handpiece groups both displayed a homogenous surface topography without obvious grooves or peaks. The data on the marginal and internal fit measured at different sites are shown in Table 2. Statistical analysis revealed that the marginal and internal discrepancies were not significantly different between the air-turbine handpiece and electric handpiece groups (P>.05). No significant difference in the internal
Pei et al
discrepancies of the 2 groups was found at the shoulder (B), axial (C and D), or occlusal (E) points (P>.05). DISCUSSION The results of the present study demonstrated that despite heavier weight, poorer grip feel, and less flexibility, the electric handpiece produced lower noise and better feeling of the tooth preparation in general and was preferred in the finishing stage of tooth preparation with smoother handling. Therefore, the null hypotheses concerning the sound levels and operator preferences were rejected. The surface roughness and crown fit tests did not reveal any significant differences between the different handpieces, so the null hypotheses regarding the surface roughness and fit of complete crowns were accepted. The choice of handpiece for tooth preparation partly depends on the dentist’s experience7 and the weight, size, shape, texture, and power of the handpiece.8 A heavier weight and larger size have been reported to be major disadvantages of electric handpieces.1 The weight of the electric handpiece used in this study was 214.5 g, while the weight of the air-turbine handpiece was only 113.5 g. This difference of weight was perceived by the 20 recruited dentists as shown by the statistically significant result of the VAS evaluation. Moreover, the electric handpiece had a larger head size and longer perimeter at the finger-holding location than the air-turbine handpiece, which may result in
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reduced access, visibility, flexibility, and grip comfort for dentists.1 The electric handpiece had stable power with high torque. The set speed was maintained, reducing vibrations and improving tactile sense,1 especially when continuous and “heavy-handed” preparation techniques are used.10 The better feeling of the tooth preparation in general with the electric handpiece was shown by the VAS evaluation. Most dentists in the present study reported that the electric handpiece offered smoother operation and preferred the electric handpiece for finishing the tooth preparation as demonstrated by the questionnaire results. Nevertheless, because of its higher rotational speed, half of the dentists chose the air-turbine handpiece during initial preparation. The continuous high-frequency handpiece noise is an occupational hazard for dentists,4 causing hearing and other health problems.5 Noise levels above 80 decibels may result in adverse consequences.5,6 In the present study, the general noise range of 58 to 73 decibels produced by both the electric and the air-turbine handpiece was within the safety zone. However, the lower noise level of the electric handpiece is an advantage for both dentists and patients. The surface roughness of a prepared tooth is an important indicator of quality.19 In the present experiment, similar roughness values were obtained with the electric or air-turbine handpieces. Additionally, no significance differences were found in the crown fit between the air-turbine and the electric handpieces. Limitations of the study include its in vitro design, avoidance of many confounding factors, and small sample size. Clinical research to evaluate other aspects of the performance of electric handpieces with a larger sample size is warranted. CONCLUSIONS Based on the findings of this in vitro study, the following conclusions were drawn: 1. Despite heavier weight, poorer grip feel, and less flexibility, the electric handpiece emitted lower noise, had better feel of the tooth preparation in general, and was preferred for its greater smoothness in the finishing step of tooth preparation than the air-turbine handpiece. 2. The surface roughness of the prepared teeth and the crown fit between the teeth and ceramic crown were not affected by the choice of air-turbine or electric handpiece.
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REFERENCES 1. Kenyon BJ, Van Zyl I, Louie KG. Comparison of cavity preparation quality using an electric motor handpiece and an air turbine dental handpiece. J Am Dent Assoc 2005;136:1101-5; quiz 1166. 2. Choi C, Driscoll CF, Romberg E. Comparison of cutting efficiencies between electric and air-turbine dental handpieces. J Prosthet Dent 2010;103:101-7. 3. Rotella M, Ercoli C, Funkenbusch PD, Russell S, Feng C. Performance of single-use and multiuse diamond rotary cutting instruments with turbine and electric handpieces. J Prosthet Dent 2014;111:56-63. 4. Ma KW, Wong HM, Mak CM. Dental environmental noise evaluation and health risk model construction to dental professionals. Int J Environ Res Public Health 2017;14. 5. Qsaibati ML, Ibrahim O. Noise levels of dental equipment used in dental college of Damascus University. Dent Res J (Isfahan) 2014;11:624-30. 6. Sampaio Fernandes JC, Carvalho AP, Gallas M, Vaz P, Matos PA. Noise levels in dental schools. Eur J Dent Educ 2006;10:32-7. 7. Campbell SC. Are friends electric?: a review of the electric handpiece in clinical dental practice. Dent Update 2013;40:9-200. 8. Christensen GJ. Are electric handpieces an improvement? J Am Dent Assoc 2002;133:1433-4. 9. Benjamin SD. Evolving technologies for improved ergonomics: selecting an appropriate electric handpiece. Pract Proced Aesthet Dent 2003;15:400-1. 10. Siegel SC, von Fraunhofer JA. Dental cutting with diamond burs: heavyhanded or light-touch? J Prosthodont 1999;8:3-9. 11. Ercoli C, Rotella M, Funkenbusch PD, Russell S, Feng C. In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part II: electric handpiece and comparison with turbine. J Prosthet Dent 2009;101:319-31. 12. Wettstein F, Sailer I, Roos M, Hammerle CH. Clinical study of the internal gaps of zirconia and metal frameworks for fixed partial dentures. Eur J Oral Sci 2008;116:272-9. 13. Karatasli O, Kursoglu P, Capa N, Kazazoglu E. Comparison of the marginal fit of different coping materials and designs produced by computer aided manufacturing systems. Dent Mater J 2011;30:97-102. 14. Kohorst P, Brinkmann H, Li J, Borchers L, Stiesch M. Marginal accuracy of four-unit zirconia fixed dental prostheses fabricated using different computer-aided design/computer-aided manufacturing systems. Eur J Oral Sci 2009;117:319-25. 15. Zeltner M, Sailer I, Muhlemann S, Ozcan M, Hammerle CH, Benic GI. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit. J Prosthet Dent 2017;117:354-62. 16. Cunali RS, Saab RC, Correr GM, Cunha LFD, Ornaghi BP, Ritter AV, et al. Marginal and internal adaptation of zirconia crowns: a comparative study of assessment methods. Braz Dent J 2017;28:467-73. 17. Kadanakuppe S, Bhat PK, Jyothi C, Ramegowda C. Assessment of noise levels of the equipments used in the dental teaching institution, Bangalore. Indian J Dent Res 2011;22:424-31. 18. Riccitiello F, Amato M, Leone R, Spagnuolo G, Sorrentino R. In vitro evaluation of the marginal fit and internal adaptation of zirconia and lithium disilicate single crowns: micro-CT comparison between different manufacturing procedures. Open Dent J 2018;12:160-72. 19. Geminiani A, Abdel-Azim T, Ercoli C, Feng C, Meirelles L, Massironi D. Influence of oscillating and rotary cutting instruments with electric and turbine handpieces on tooth preparation surfaces. J Prosthet Dent 2014;112: 51-8. 20. Lovgren N, Roxner R, Klemendz S, Larsson C. Effect of production method on surface roughness, marginal and internal fit, and retention of cobaltchromium single crowns. J Prosthet Dent 2017;118:95-101. 21. Li YQ, Wang H, Wang YJ, Chen JH. Effect of different grit sizes of diamond rotary instruments for tooth preparation on the reevetion and adaptation of complete coverage restorations. J Prosthet Dent 2012;107:86-93. Corresponding author: Dr Yi Lu Department of Prosthodontics College of Stomatology Xi’an Jiaotong University 98 Xiwu Road, Xi’an 710004 PR CHINA Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.11.001
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Comparison of crown fit and operator preferences between tooth preparation with electric and air-turbine handpieces Dan-dan Pei, MD,a Yu-chen Meng, BS,b Ahmed S. Fayed, MS,c Yu-fei You, MS,d Zi-xiao Wu, BS,e and Yi Lu, PhDf
ABSTRACT Statement of problem. Tooth preparations for ceramic crowns require precision and accuracy, which may be influenced by the choice of dental handpiece. However, comparisons of the accuracy of tooth preparations made with traditional air-turbine handpieces and electric handpieces are lacking. Purpose. The purpose of this in vitro study was to evaluate operator preferences and tooth preparation performance by using electric and airturbine handpieces with self-reported preferences, sound levels, surface roughness, and the fit of the crown produced. Material and methods. Twenty dentists were asked to use the air-turbine or the electric handpiece. Feedback on the noise, weight, feel of grip, flexibility, and tooth preparation in general was scored according to a visual analog scale (VAS). Additionally, the dentists were asked to complete a questionnaire on their handpiece preference. The noise of the 2 handpieces was measured by using a precision sound level meter. The surface roughness of 10 teeth was measured by using a profilometer. The other 18 teeth were prepared to measure the marginal and internal fit of ceramic crowns by the replica technique. The VAS scores of operator preferences were analyzed with the Wilcoxon signed ranks test. Decibel levels were analyzed with the Mann-Whitney U test. The McNemar test was used to compare the ratio of preferred handpiece. The surface roughness and marginal and internal fit were analyzed with the independent t test to determine significant differences (all a=.05). Results. The electric handpiece was heavier, had a poorer grip feel, was less flexible (P<.001), produced lower noise and better feeling of the tooth preparation in general (P<.001), and was preferred in the finishing stage for its greater smoothness (P<.05). The noise produced by the electric handpiece was lower during both idling and tooth preparation at 15-cm, 30-cm, and 45-cm distances (P<.01). The electric handpiece produced surface roughness values (Sa) similar to those of the air-turbine handpiece (P>.05). No significant differences were noted for the marginal and internal crown fit between the air-turbine handpiece and electric handpiece groups (P>.05). Conclusions. Despite its heavier weight, poorer grip feel, and less flexibility, the electric handpiece emitted lower noise, produced better feeling of the tooth preparation in general, and was preferred in the finishing step of tooth preparation for its greater smoothness than the air-turbine handpiece. The surface roughness of the prepared teeth and the crown fit between the tooth and ceramic crown were not affected by the air-turbine or electric handpiece. (J Prosthet Dent 2019;-:---)
A high-quality tooth preparation is essential for producing a precision crown restoration in contemporary dentistry, with the choice of dental handpiece being an important factor affecting the accuracy of the tooth preparation.1 The traditional high-speed air-turbine handpiece has been used in dentistry for decades,2 and
although they are still extensively used, their low torque can cause a loss of speed (revolutions per minute) and even stall at moderate or high load.3 Dentists have also complained about other deficiencies, including the high-pitched noise,4-6 vibration, and poor concentricity.7 To overcome these disadvantages, electric
D.-d.P. and Y.-c.M. contributed equally to the work. This study was supported by grants from the National Natural Science Foundation of China (grant #81870798), the Innovation Project from Shaanxi province (grant #2016KTCL03-10), and the opening project from College of Stomatology, Xi’an Jiaotong University (grant #2018YHJB07). a Associate Professor, Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. b Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. c Former Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. d Former Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. e Postgraduate Resident, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China. f Professor and Chair, Department of Prosthodontics, College of Stomatology, Xi’an Jiaotong University, Xi’an, PR China.
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Clinical Implications Tooth preparation with an electric or air-turbine handpiece did not affect the fit of a ceramic crown. However, the significantly heavier electric handpiece was significantly quieter and smoother than the air-turbine handpiece.
motors with speed-increasing handpieces have been introduced. Compared with air-turbine handpieces, electric handpieces have a smoother operation because of their constant power and high torque,1,7 which may provide clinicians with greater tactile feedback for a more controlled cutting performance, especially for the creation of margins. Conversely, the increased size and weight of electric handpieces are shortcomings, particularly for dentists with smaller hands.8,9 When selecting a handpiece, the working efficiency, operator preference,10 and preparation results are parameters that dentists consider. Recent studies of electric handpieces have mainly focused on the cutting efficiency, and the results have demonstrated that electric handpieces are comparable or even more efficient at cutting dental hard tissue than airturbine handpieces.2,11 However, the user’s feeling and the tooth preparation performance of electric handpieces have not yet been clarified in detail. The demand for esthetics has made ceramic restoration a popular choice.12-14 The marginal and internal accuracy of fit are important criteria for the clinical success of ceramic prostheses.15,16 Thus, the present study evaluated the operator preferences and tooth preparation performance of electric handpieces compared with those of traditional air-turbine handpieces. The sound levels produced by handpieces, self-reported preferences, surface roughness, and crown fit of electric and air-turbine handpieces were evaluated to assist dentists in their choice. The null hypotheses were that no differences would be found in the operator preference scores, preference ratios, sound levels, surface roughness, or crown fit between teeth prepared with electric or air-turbine handpieces. MATERIAL AND METHODS An electric handpiece (Restorative Classic CA 1:5; BienAir Dental) and an air-turbine handpiece (TE-95RM; W&H Dentalwerk GmbH) were used for the tests. The electric handpiece was used at its maximum speed of 200 000 revolutions per minute (40 000 motor speed with a 1:5 ratio).3 A total of 54 intact impacted human third molars were obtained from the Department of Oral and Maxillofacial Surgery, School and Hospital of Stomatology, Xi’an Jiaotong University, after informed consent THE JOURNAL OF PROSTHETIC DENTISTRY
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was obtained from the donors and approval by the ethics committee. The teeth were stored in 0.02% sodium azide at 4 C for less than 3 months before use. To evaluate the operator preferences, 20 experienced dentists from the Department of Prosthodontics, School and Hospital of Stomatology, Xi’an Jiaotong University, were enrolled in the study. The range of clinical experience varied from 6 to 20 years (with a mean clinical experience of 15.4 years). The dentists were instructed to use the air-turbine or electric handpiece with hand grip gestures (Fig. 1) during idling and tooth preparation and to record their user experiences. Feedback in terms of noise level, weight, feel of the grip, flexibility, and general feeling of the tooth preparation was scored according to a visual analog scale (VAS). The dentists were asked to complete a questionnaire on their handpiece preference for the initial preparation, finishing preparation, and smooth operation. All measurements were conducted in a separate room with good sound insulation to exclude environmental interference. The handpiece noise emission was detected by using a precision sound level meter (6288; Aihua Instruments Co, Ltd).17 The sound levels during handpiece idling were first measured at 15-cm, 30-cm, and 45-cm distances from the prepared tooth for each handpiece. The sound levels during tooth preparation with salivary suction were then measured at 15-cm, 30-cm, and 45-cm distances from the prepared tooth. The noise measurement for each group was repeated 6 times, and each interval was 5 seconds. To measure the surface roughness after tooth preparation, 10 teeth were divided into air-turbine and electric handpiece groups and prepared on dental simulators (NISSIM Type 1; NISSIN) by the same operator (D.-d.P.) with 6 years of clinical experience following complete crown preparation guidelines18 with new diamond rotary instruments (Table 1). The surface roughness of the prepared specimens was then evaluated quantitatively by using a profilometer (PS50; Nanovea). The sensor was placed perpendicular to the tooth surface. Three measurements were analyzed for each specimen, and each measurement area was 280×210 mm. A 60×60-mm Gaussian filter was used to remove errors. The mean surface roughness of each specimen was represented by Sa values.19 The crown fit test was conducted by evaluating the marginal and internal fit of ceramic crowns. A total of 18 teeth were divided into 2 groups. Following the complete crown preparation guidelines, the teeth were prepared in manikin heads with the air-turbine or electric handpiece by the same operator (D.-d.P.) with 6 years of clinical experience. After finishing the tooth preparations, Cercon II ceramic crowns (Dentsply Sirona) with a preset internal gap space of 80 mm in the occlusal and axial plane and 20 mm at the margins were designed and Pei et al
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Figure 1. A, Air-turbine handpiece. B, Electric handpiece. Table 1. Characteristics of diamond rotary instrument used Diameter of Diamond Particles (mm)
Manufacturer
Number
Coarse
125
Diatech
856-314-014-9-ML
Coarse
125
Diatech
881-314-012-8-ML
Coarse
125
Diatech
379-314-023-5-ML
Fine
40
Diatech
856-314-016-8-F
Extra fine
20
Diatech
379-314-023-5-XF
Extra fine
20-30
MANI
TR-25EF
fabricated by the same technician for each individual abutment tooth. Then, the marginal and internal fit of each crown was measured as the internal gap between the crown and the prepared tooth by using the replica technique with silicone impression material (HonigumLight, Honigum-Putty; DMG) as described previously.15,20 Briefly, each crown was filled with a yellow light-body silicone material and placed onto the corresponding tooth under a constant force of 50 N. After polymerization for 5 minutes, the tooth was carefully removed, and purple heavy-body silicone rubber material was then applied instead of the prepared tooth. Finally, the crown was removed, and the purple heavy-body silicone rubber material was applied on the crown side to form a sandwich silicone replica. The replicas were cross-sectioned into thicknesses of 1 mm at the center of and perpendicular to the occlusal surface. These sections were measured at ×100 magnification under a stereomicroscope (M250FA; Leica) by 1 blinded investigator (Y.-c.M.). The light-body thickness represented the discrepancy between the crown surface and the abutment tooth. Measurements were conducted at 10 points by following an established protocol21 as shown in Figure 2: A1 and A2 represent the marginal discrepancy; B1 and B2 represent the shoulder discrepancy; C1, C2, D1, and D2 represent the axial discrepancy; and E1 and E2 represent the occlusal discrepancy. All the statistical calculations were conducted by using a statistical software program (PASW Statistics, v18.0; Pei et al
Figure 2. Sites of evaluation of crown fit. A1, A2: margin. B1, B2: shoulder. C1, C2, D1, D2: axial wall. E1, E2: occlusal surface.
Groups
Grit
Tooth preparation feeling
*
Flexibility
*
Hand grip feeling
*
Weight
*
Noise of preparation
*
Noise of idling
* 0
2
4
6
8
10
Index Electric handpiece
Air-turbine handpiece
Figure 3. VAS scores of operator preferences for air-turbine and electric handpieces. *Statistically significant (P<.05).
SPSS Inc) (a=.05). The Wilcoxon signed-rank test was used to compare the differences in the VAS scores of the operator preferences because the paired data did not satisfy the parametric methods. The McNemar test was used to compare the paired ratios of the preferred handpiece. The independent decibel level data did not satisfy the parametric methods, so the Mann-Whitney U test was applied to the analysis. Statistical analyses of the THE JOURNAL OF PROSTHETIC DENTISTRY
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Preference in initial preparation
Electric 35%
70
* *
60 55 15
30
45
Traverse length (cm) Air-turbine handpiece
Electric handpiece
A
A dB 75
Sound level (dB)
Preference in finishing preparation
Both 10%
*
*
70
*
65 60 55 50
Electric 80%
15
30
B
Electric handpiece
B Figure 5. Sound levels of air turbine and electric handpieces at 15-cm, 30-cm, and 45-cm distances. A, During idling. B, During tooth preparation. *Statistically significant (P<.05).
Preference in smooth operation
Both 10%
Electric 80%
C Figure 4. Distribution of total variables. A, Initial preparation. B, Finishing preparation. C, Smooth operation.
surface roughness and marginal and internal fit were performed by using the independent t test after the normal distribution and homogeneity of variance tests. RESULTS The VAS scores of the operator preferences are illustrated in Figure 3. The Wilcoxon signed-rank test indicated that THE JOURNAL OF PROSTHETIC DENTISTRY
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Traverse length (cm) Air-turbine handpiece
Air-turbine 10%
-
*
65
50
Air-turbine 50%
Air-turbine 10%
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dB 75
Sound level (dB)
Both 15%
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the air-turbine handpiece noise was significantly higher than that of the electric handpiece both during idling (Z=-5.377, P<.001) and tooth preparation (Z=-5.446, P<.001), while the electric handpiece was relatively heavier than the air-turbine handpiece (Z=-5.377, P<.001). The air-turbine handpiece was better than the electric handpiece in terms of grip feel (Z=-5.452, P<.001) and flexibility (Z=-5.519, P<.001), while the electric handpiece was better than the air-turbine handpiece for general tooth preparation (Z=-5.516, P<.001). The ratio of the dentists’ preferred handpieces varied significantly for the initial preparation, finishing preparation, and smooth operation (P<.05). Figure 4 illustrates the distribution of the total variables on the 3 questions. Although only 35% of the dentists chose the electric handpiece, 15% thought both handpieces were acceptable during initial preparation, while 80% preferred the electric handpiece for finishing. Overall, 80% of the dentists reported that the electric handpiece offered smooth operation in the working process. The mean values and standard deviations of the sound levels measured at 15-cm, 30-cm, and 45-cm Pei et al
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Figure 6. Three-dimensional surface profile. A, Air-turbine handpiece group. B, Electric handpiece group.
Table 2. Gap thickness (mean ±standard deviation) between crown and abutment tooth after preparation by air-turbine and electric handpieces (n=9) Marginal Groups
Internal
Marginal (A)
Shoulder (B)
Axial (C)
Axial (D)
Occlusal (E)
Total
Air-turbine
116.1 ±13.4
123.7 ±24.0
84.5 ±20.7
101.1 ±26.7
210.6 ±27.0
130.0 ±17.0
Electric
106.5 ±12.3
137.5 ±13.5
73.3 ±21.1
107.1 ±22.5
186.8 ±27.7
126.2 ±14.0
No significant difference among groups (P>.05).
distances from the prepared tooth are shown in Figure 5. The highest decibel level was produced by the air-turbine handpiece at the15-cm distance during tooth preparation, and the lowest decibel level was produced by the electric handpiece at the 45-cm distance during idling. The statistical analysis revealed significant differences in the decibel levels produced by the 2 handpieces during idling at the 15-cm (Z=-2.908, P<.01), 30-cm (Z=-2.882, P<.01), and 45-cm (Z=-2.908, P<.01) distances. The decibel levels of tooth preparation were also significantly different between the air-turbine handpiece and electric handpiece at the 15-cm (Z=-2.898, P<.01), 30-cm (Z=-2.934, P<.01), and 45-cm (Z=-2.898, P<.01) distances. The tooth surface roughness prepared by the airturbine handpiece had Sa values (mean ±standard deviation) of 1.58 ±0.18, and the Sa values of the electric handpiece were 1.49 ±0.25. No statistically significant difference for Sa was found (t=0.908, P>.05). Figure 6 presents 3D graphs (scale: x-axis 0.005 mm per mark, y-axis 0.002 mm per mark, and z-axis 0.01 mm per mark) of the surface microstructure. The air-turbine handpiece and electric handpiece groups both displayed a homogenous surface topography without obvious grooves or peaks. The data on the marginal and internal fit measured at different sites are shown in Table 2. Statistical analysis revealed that the marginal and internal discrepancies were not significantly different between the air-turbine handpiece and electric handpiece groups (P>.05). No significant difference in the internal
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discrepancies of the 2 groups was found at the shoulder (B), axial (C and D), or occlusal (E) points (P>.05). DISCUSSION The results of the present study demonstrated that despite heavier weight, poorer grip feel, and less flexibility, the electric handpiece produced lower noise and better feeling of the tooth preparation in general and was preferred in the finishing stage of tooth preparation with smoother handling. Therefore, the null hypotheses concerning the sound levels and operator preferences were rejected. The surface roughness and crown fit tests did not reveal any significant differences between the different handpieces, so the null hypotheses regarding the surface roughness and fit of complete crowns were accepted. The choice of handpiece for tooth preparation partly depends on the dentist’s experience7 and the weight, size, shape, texture, and power of the handpiece.8 A heavier weight and larger size have been reported to be major disadvantages of electric handpieces.1 The weight of the electric handpiece used in this study was 214.5 g, while the weight of the air-turbine handpiece was only 113.5 g. This difference of weight was perceived by the 20 recruited dentists as shown by the statistically significant result of the VAS evaluation. Moreover, the electric handpiece had a larger head size and longer perimeter at the finger-holding location than the air-turbine handpiece, which may result in
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reduced access, visibility, flexibility, and grip comfort for dentists.1 The electric handpiece had stable power with high torque. The set speed was maintained, reducing vibrations and improving tactile sense,1 especially when continuous and “heavy-handed” preparation techniques are used.10 The better feeling of the tooth preparation in general with the electric handpiece was shown by the VAS evaluation. Most dentists in the present study reported that the electric handpiece offered smoother operation and preferred the electric handpiece for finishing the tooth preparation as demonstrated by the questionnaire results. Nevertheless, because of its higher rotational speed, half of the dentists chose the air-turbine handpiece during initial preparation. The continuous high-frequency handpiece noise is an occupational hazard for dentists,4 causing hearing and other health problems.5 Noise levels above 80 decibels may result in adverse consequences.5,6 In the present study, the general noise range of 58 to 73 decibels produced by both the electric and the air-turbine handpiece was within the safety zone. However, the lower noise level of the electric handpiece is an advantage for both dentists and patients. The surface roughness of a prepared tooth is an important indicator of quality.19 In the present experiment, similar roughness values were obtained with the electric or air-turbine handpieces. Additionally, no significance differences were found in the crown fit between the air-turbine and the electric handpieces. Limitations of the study include its in vitro design, avoidance of many confounding factors, and small sample size. Clinical research to evaluate other aspects of the performance of electric handpieces with a larger sample size is warranted. CONCLUSIONS Based on the findings of this in vitro study, the following conclusions were drawn: 1. Despite heavier weight, poorer grip feel, and less flexibility, the electric handpiece emitted lower noise, had better feel of the tooth preparation in general, and was preferred for its greater smoothness in the finishing step of tooth preparation than the air-turbine handpiece. 2. The surface roughness of the prepared teeth and the crown fit between the teeth and ceramic crown were not affected by the choice of air-turbine or electric handpiece.
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REFERENCES 1. Kenyon BJ, Van Zyl I, Louie KG. Comparison of cavity preparation quality using an electric motor handpiece and an air turbine dental handpiece. J Am Dent Assoc 2005;136:1101-5; quiz 1166. 2. Choi C, Driscoll CF, Romberg E. Comparison of cutting efficiencies between electric and air-turbine dental handpieces. J Prosthet Dent 2010;103:101-7. 3. Rotella M, Ercoli C, Funkenbusch PD, Russell S, Feng C. Performance of single-use and multiuse diamond rotary cutting instruments with turbine and electric handpieces. J Prosthet Dent 2014;111:56-63. 4. Ma KW, Wong HM, Mak CM. Dental environmental noise evaluation and health risk model construction to dental professionals. Int J Environ Res Public Health 2017;14. 5. Qsaibati ML, Ibrahim O. Noise levels of dental equipment used in dental college of Damascus University. Dent Res J (Isfahan) 2014;11:624-30. 6. Sampaio Fernandes JC, Carvalho AP, Gallas M, Vaz P, Matos PA. Noise levels in dental schools. Eur J Dent Educ 2006;10:32-7. 7. Campbell SC. Are friends electric?: a review of the electric handpiece in clinical dental practice. Dent Update 2013;40:9-200. 8. Christensen GJ. Are electric handpieces an improvement? J Am Dent Assoc 2002;133:1433-4. 9. Benjamin SD. Evolving technologies for improved ergonomics: selecting an appropriate electric handpiece. Pract Proced Aesthet Dent 2003;15:400-1. 10. Siegel SC, von Fraunhofer JA. Dental cutting with diamond burs: heavyhanded or light-touch? J Prosthodont 1999;8:3-9. 11. Ercoli C, Rotella M, Funkenbusch PD, Russell S, Feng C. In vitro comparison of the cutting efficiency and temperature production of ten different rotary cutting instruments. Part II: electric handpiece and comparison with turbine. J Prosthet Dent 2009;101:319-31. 12. Wettstein F, Sailer I, Roos M, Hammerle CH. Clinical study of the internal gaps of zirconia and metal frameworks for fixed partial dentures. Eur J Oral Sci 2008;116:272-9. 13. Karatasli O, Kursoglu P, Capa N, Kazazoglu E. Comparison of the marginal fit of different coping materials and designs produced by computer aided manufacturing systems. Dent Mater J 2011;30:97-102. 14. Kohorst P, Brinkmann H, Li J, Borchers L, Stiesch M. Marginal accuracy of four-unit zirconia fixed dental prostheses fabricated using different computer-aided design/computer-aided manufacturing systems. Eur J Oral Sci 2009;117:319-25. 15. Zeltner M, Sailer I, Muhlemann S, Ozcan M, Hammerle CH, Benic GI. Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit. J Prosthet Dent 2017;117:354-62. 16. Cunali RS, Saab RC, Correr GM, Cunha LFD, Ornaghi BP, Ritter AV, et al. Marginal and internal adaptation of zirconia crowns: a comparative study of assessment methods. Braz Dent J 2017;28:467-73. 17. Kadanakuppe S, Bhat PK, Jyothi C, Ramegowda C. Assessment of noise levels of the equipments used in the dental teaching institution, Bangalore. Indian J Dent Res 2011;22:424-31. 18. Riccitiello F, Amato M, Leone R, Spagnuolo G, Sorrentino R. In vitro evaluation of the marginal fit and internal adaptation of zirconia and lithium disilicate single crowns: micro-CT comparison between different manufacturing procedures. Open Dent J 2018;12:160-72. 19. Geminiani A, Abdel-Azim T, Ercoli C, Feng C, Meirelles L, Massironi D. Influence of oscillating and rotary cutting instruments with electric and turbine handpieces on tooth preparation surfaces. J Prosthet Dent 2014;112: 51-8. 20. Lovgren N, Roxner R, Klemendz S, Larsson C. Effect of production method on surface roughness, marginal and internal fit, and retention of cobaltchromium single crowns. J Prosthet Dent 2017;118:95-101. 21. Li YQ, Wang H, Wang YJ, Chen JH. Effect of different grit sizes of diamond rotary instruments for tooth preparation on the reevetion and adaptation of complete coverage restorations. J Prosthet Dent 2012;107:86-93. Corresponding author: Dr Yi Lu Department of Prosthodontics College of Stomatology Xi’an Jiaotong University 98 Xiwu Road, Xi’an 710004 PR CHINA Email: [email protected] Copyright © 2019 by the Editorial Council for The Journal of Prosthetic Dentistry. https://doi.org/10.1016/j.prosdent.2019.11.001
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